\begin{figure}[H]
\centering
\begin{subfigure}[b]{.4\textwidth}
\centering
\figscale{
  \begin{tikzpicture}[%
    >=stealth,
    shorten >=1pt,
    node distance=2cm,
    on grid,
    auto,
    state/.append style={minimum size=2em},
    thick,
    scale=0.4
  ]
    \node[state, rectangle, align=center] (N1) {$A$\\$\textcolor{BrickRed}{EX(\textcolor{Blue}{\$B})}$};
    \node[state] (N2) [below left of=N1] {$B$};
    \node[state] (N3) [below right of=N1] {$C$};

    \path[->, BrickRed]
              (N1) edge node [above left] {$\textcolor{Blue}{\$B}$} (N2);

    \path[->]
              (N1) edge node {} (N3);
  \end{tikzpicture}
}
\caption{$EX(\$B)$}
\end{subfigure}
\begin{subfigure}[b]{.4\textwidth}
\centering
\figscale{
  \begin{tikzpicture}[%
    >=stealth,
    shorten >=1pt,
    node distance=2cm,
    on grid,
    auto,
    state/.append style={minimum size=2em},
    thick,
    scale=0.4
  ]
    \node[state, rectangle, align=center] (N1) {$A$\\$\textcolor{BrickRed}{AX(\textcolor{Cerulean}{EX(\textcolor{RoyalPurple}{EX(\textcolor{OliveGreen}{\$E})})})}$};
    \node[state] (N2) at (-4, -4) {$B$};
    \node[state] (N3) at (4, -4) {$C$};
    \node[state] (N4) at (0, -8) {$D$};
    \node[state] (N5) at(4, -8) {$E$};

\path[->, BrickRed]
	(N1) edge node [above left, pos=0.75] {$\textcolor{Cerulean}{EX(\textcolor{RoyalPurple}{EX(\textcolor{OliveGreen}{\$E})})}$} (N2)
	(N1) edge node [above right, pos=0.75] {$\textcolor{Cerulean}{EX(\textcolor{RoyalPurple}{EX(\textcolor{OliveGreen}{\$E})})}$} (N3);

\path[->, Cerulean]
	(N2) edge node [below left, pos=0.25] {$\textcolor{RoyalPurple}{EX(\textcolor{OliveGreen}{\$E})}$} (N4)
	(N3) edge node [below right, pos=0.25] {$\textcolor{RoyalPurple}{EX(\textcolor{OliveGreen}{\$E})}$} (N4);

\path[->, RoyalPurple]
	(N4) edge node [below] {$\textcolor{OliveGreen}{\$E}$} (N5);
  \end{tikzpicture}
}
\caption{$AX(EX(EX(\$E)))$}
\end{subfigure}
\caption{Exemples de colorations}
\label{fig:Coloration}
\end{figure}